docs: def get_mean_and_stddevs(self, sites, rup, dists, imt, stddev_types):
          """
          See :meth:`superclass method
          <.base.GroundShakingIntensityModel.get_mean_and_stddevs>`
          for spec of input and result values.
          """
          assert all(stddev_type in self.DEFINED_FOR_STANDARD_DEVIATION_TYPES
                     for stddev_type in stddev_types)
  
          C = self.COEFFS[imt]
          mean = self._compute_mean(C, rup.mag, dists.rjb)
          stddevs = self._compute_stddevs(C, rup.mag, dists.rjb, imt,
                                          stddev_types)
  
          # apply decay factor for 3 and 4 seconds (not originally supported
          # by the equations)
          if imt.period == 3.0:
              mean /= 0.612
          if imt.period == 4.0:
              mean /= 0.559
  
          return mean, stddevs